1. Field of the Invention
The present invention generally relates to a piston type refrigerant compressor and, more particularly, to a swash plate type compressor with a variable displacement mechanism suitable for use in an automotive air conditioning system.
2. Description of the Prior Art
A swash plate type refrigerant compressor with a variable displacement mechanism suitable for use in an automotive air conditioning system is disclosed in Japanese Patent Application Publication No. 63-93480. Referring to FIG. 1, an outer shell of the compressor is formed by front housing 1, front valve plate 9, cylinder block 3, rear valve plate 4, and rear housing 5, which are made of an aluminum alloy. Cylinder block 3 comprises front cylinder block 3a and rear cylinder block 3b which abut each other. Front housing 1 is mounted through front valve plate 9 on one side of cylinder block 3, and rear housing 5 is mounted through rear valve plate 4 on the other side of cylinder block 3. These shell components are coupled in a unit by a plurality of bolts 6.
A plurality of cylinders 7, arranged in parallel with each other, and chamber 8 are formed by front and rear cylinder blocks 3a and 3b within cylinder block 3. Further, first bearing, 10 and second bearing 11 are disposed in cylinder block 3 and rear housing 5, respectively, to rotatably support drive shaft 12. Drive shaft 12 is arranged coaxially with the annular arrangement of cylinders 7. One end portion 13 of drive shaft 12 extends to the outside of front housing 1 through drive shaft sealing bearing 14 mounted on front housing 1. Exposed end portion 13 is connected to an electromagnetic clutch (not shown), so that the rotational torque of an automotive vehicle engine may be transmitted to drive shaft 12 through the electromagnetic clutch.
Piston 17 defines a front side working chamber 15 and a rear side working chamber 16 in cooperation with an inner surface of each cylinder 7 and is reciprocatingly inserted into each cylinder 7. Thus, each piston 17 may be slidably reciprocated by swash plate 18 disposed within crank chamber 8.
Swash plate 18 has a projection portion at its central region, and arm 19 is formed in the projection portion. Planar plate portion 20 is formed in drive shaft 12 at a position corresponding to arm 19 of swash plate 18. Swash plate 18 is obliquely mounted on drive shaft 12 with planar plate portion 20 engaged with arm 19. Also, pin 21 is fixed to the projection portion of swash plate 18. Pin 21 is engaged through a collar with elongated hole 22 formed in planar plate portion 20 of drive shaft 12. In this configuration, swash plate 18 is shifted between a position in which the slant angle is large and a position in which the slant angle is small, while pin 21 of swash plate 18 slides within elongated hole 22. The capacity of the compressor is dependent upon the slant angle of swash plate 18. When the slant angle of swash plate 18 is increased, the stroke length of piston 17 in cylinder 7 is maximized, and the capacity of the compressor is decreased. The rotational force of drive shaft 12 is transmitted to swash plate 18 through the engagement between planar plate portion 20 and arm 19. Swash plate 18 is driven to rotate about the axis of drive shaft 12 together with drive shaft 12 and to move in the axial direction of drive shaft 12. Thus, swash plate 18 is swung between a rightwardly upward inclination and a rightwardly downward inclination.
The circumferential peripheral portion of swash plate 18 is connected to piston 17 through a pair of shoes 23. Swash plate 18 is inserted slidingly into the space between the pair of shoes 23. Shoes 23 form a single spherical shape when in contact with swash plate 18 and rotatably mounted on recesses formed in piston 17 in a complementary manner. Accordingly, the swing motion concomitant with the rotation of swash plate 18 is transmitted to piston 17 through shoes 23, while the rotational motion component of swash plate 18 is released by shoes 23. Only the swing motion of swash plate 18 is converted into the reciprocating motion of piston 17 which is reciprocated within cylinder 7, so that the volume of front side working chamber 15 and rear side working chamber 16 are alternately increased and decreased.
Front housing 1 defines front suction chamber 24 and front discharge chamber 25. Drive shaft sealing bearing 14 is provided between front suction chamber 24, drive shaft 12, and front housing 1 to prevent the refrigerant, e.g., a mixture of refrigerant and lubricant, from leaking out. From suction chamber 24 is in communication with crank chamber 8 through a hole formed in front valve plate 9 and front passage 26 formed in cylinder block 3. Further, front suction chamber 24 is in communication with front side working chamber 15 through front suction hole 27 formed in front valve plate 9. Also, front discharge chamber 25 is in communication with front side working chamber 15 through front discharge hole 28 formed in front valve plate 9.
Front suction valve 29 in the form of a sheet is provided on the surface of front valve plate 9 within front side working chamber 15, so that front suction valve 29 is opened when piston 17 is rightwardly moved. Sheet-like discharge valve 30 is provided on the surface of front valve plate 9 within discharge chamber 25, so that discharge valve 30 is opened when piston 17 is leftwardly moved. Discharge valve 30 is converted by front valve retainer 31.
Rear housing 5 defines rear suction chamber 32 and rear discharge chamber 33. Rear suction chamber 32 is in communication with crank chamber 8 through a hole formed in rear valve plate 4 and rear passage 34 formed in cylinder block 3. Further, rear suction chamber 32 is in communication with rear side working chamber 16 through rear suction hole 35. Rear discharge chamber 33 is in communication with rear side working chamber 16 through rear discharge hole 36 formed in rear valve plate 4. Rear suction valve 37, rear discharge valve 38, and rear valve retainer 39 are mounted on rear valve plate 4 in a similar manner to that described for the corresponding front elements.
Switching valve 40 and control chamber.41 also are provided in rear housing 5. Slider 42 is rotatably mounted on drive shaft 12 to be slidable in the axial direction of drive shaft 12. Slider 42 is provided with spherical support portion 43 at one end thereof close to planar plate portion 20 of drive shaft 12. Spherical support portion 43 permits the central portion of swash plate 18 to rotate about the axis of drive shaft 12 and to move in the axial direction. Slider 42 has flange portion 44 which is connected to one end of spool 46 through second thrust bearing 45.
Spool 46 has annular piston portion 47 which is formed at the outer end of spool 46 and is inserted into rear suction chamber 32 to divide the chamber into rear suction chamber 32 and control chamber 41, and cylindrical portion 48 which extends coaxially with drive shaft 12 and slider 42 from piston portion 47 to the interior of cylinder block 3. Cylindrical portion 48 of spool 46 is slidably inserted into cylindrical portion 3d formed in rear cylinder block 3b. Thus, the motion of spool 46 in the axial direction is transmitted to slider 42 through second thrust bearing 45 and flange portion 44. First thrust bearing 49 is also provided on drive shaft 12 on the front side of planar plate portion 20 and is clamped between planar plate portion 20 of drive shaft 12 and retainer shoulder 3c provided in front cylinder block 3a to impart a thrust to drive shaft 12.
Referring to FIG. 2a, piston 17 includes piston head 17b at each end. Piston 17 is formed such that the middle portion of piston 17, namely coupling portion 17c which is substantially semicircular in section and through which two piston heads 17b are coupled together, is operatively connected with both sides of the peripheral portion of swash plate 18 through shoes 23. Supporting portion 17d which is formed inside of coupling portion 17c supports shoes 23.
The operation of the compressor will now be described. Referring to FIG. 1, when the above-described electromagnetic clutch is engaged to transmit the drive torque from the automotive vehicle engine, drive shaft 12 begins to rotate within cylinder block 3. The rotation of drive shaft 12 is transmitted to arm 19 and swash plate 18 to rotate the latter. Because swash plate 18 is slanted relative to drive shaft 12, swash plate 18 is swung in accordance with the rotation of drive shaft 12, so that piston 17 is reciprocated within cylinder 7 in accordance with this swing motion.
When the discharge displacement of the compressor must be kept at a maximum level, switching valve 40 is switched over to place control chamber 41 in communication with rear discharge chamber 33. Then the pressure applied to the right side of piston portion 47 of spool 46 is higher than the pressure applied to the left side, so that spool 46 moves leftwardly. At the same time, the central position of swash plate 18 and slider 42 are moved leftwardly, so that the left end of slider 42 is brought into contact with planar plate portion 20 of drive shaft 12. By the leftward movement of swash plate 18, the projection portion of swash plate 18 having pin 21 is moved leftwardly relative to planar plate portion 20 of drive shaft 12, ,so that pin 21 is moved along elongated hole 22 of planar plate portion 20 toward the left upward end. In accordance with the left upward movement of pin 21, swash plate 18 is rotated about the center of spherical support portion 43 of slider 42 to create a large slant angle.
Further, piston 17 is reciprocated within cylinder 7. As piston 17 reciprocates, the refrigerant is alternately drawn into and compressed within front and rear side working chambers 15 and 16.
The refrigerant is introduced to the compressor from the refrigerant cycle through crank chamber 8 to front and rear suction chambers 24 and 32 and exits to the refrigerant cycle through front and rear discharge chambers 25 and 33. As described above, swash plate 18 is moved in the axial direction of drive shaft 12, so that the slant angle is changed and the central position is located substantially at the center in the longitudinal direction of cylinder 7. Therefore, as piston 17 reciprocates through a complete stroke, a loss of compression is avoided in front and rear side working chambers 15 and 16. The refrigerant compressed in the same manner is discharged from either of front and rear side working chambers 15 and 16. Accordingly, the flow refrigerant is generated in either of front and rear side working chamber 15 and 16, drive shaft sealing bearing 14 is in contact with that flow refrigerant, and the heat generated due to the friction with drive shaft 12 is removed by the refrigerant.
When the discharge displacement of the compressor must be kept at a minimum level, the switching over of switching Valve 40 places control chamber 41 in communication with rear suction chamber 32. When drive shaft 12 is rotated under this condition, swash plate 18 causes piston 17 to move rightwardly. As a result of the reactive force applied to piston 17, a force decreasing the inclination angle of swash plate 18 is applied to swash plate 18. Namely, the force rotating swash plate 18 in a counterclockwise direction is applied to swash plate 18 by piston 17.
The force applied to swash plate 18 is limited because pin 21 is slidingly engaged with elongated hole 22, and a force pressing the central position of swash plate 18 to the right in the axial direction of drive shaft 12 is created. The force component is transmitted to spool 46 through slider 42. As described above, because the pressure difference is not generated between both sides of the piston portion 47 of spool 46, piston portion 47 moves rightwardly. Thus, the inclination angle of swash plate 18 is decreased and, at the same time, the central portion of swash plate 18 is moved toward rear side working chamber 16. The dead center position in rear side working chamber 16 is kept at substantially the same position as in the case of the above-described maximum displacement operation. Further, each piston 17 includes inner surface 300c formed on the inside thereof. A clearance of about 2 to 3 mm exists between radial end extremity 18a of swash plate 18 and each piston 17 because a swash plate compressor with variable displacement requires a relatively large clearance to vary the capacity of compression by changing the piston stroke.
Unfortunately, this relatively large clearance allows piston 17 to rotate within cylinder 7 and creates noise due to collisions between inner surface 300c of piston 17 and radial end extremity 18a of swash plate 18. Therefore, each piston 17 is provided with rotation prevention means 300 integrally formed on the center portion of piston 17 and extending radially therefrom. Referring to FIGS. 2a and 2b, rotation prevention means 300 includes first surface 300a formed on the upper surface thereof and second surface 300b formed on the radial end thereof. Rotation prevention means 300 is adapted to engage recess 310 formed in the wall of each cylinder 7. It will be seen that rotation prevention means 300 and recess 310 cooperate to prevent piston 7 from rotating about its own axis, thereby suppressing noise during operation of the compressor.
In this configuration, however, both the surface of recess 310 of cylinder block 3 and first surface 300a of rotation prevention means 300 are preferably formed as fine surfaces by machining in a finishing process in order to smoothly slide against each other. To cut and grind the surface of recess 310 of cylinder block 3 with a lathe and finishing tool consumes much time and energy because recess 310 is provided inside of cylinder block 3 which includes various projections impeding milling. Further, these above-described surfaces are relatively broad. As a result, this compressor has reduced productivity and a high manufacturing cost.